Fix a large bunch of warnings, and there are still mistakes that should be fixed before the SC release

instead of introducing RUNTIME_distributed_barrier

MORSE_Distributed_size, MORSE_Distributed_rank so that applications do not
hardcode the use of MPI.

Introduce RUNTIME_distributed_rank, RUNTIME_distributed_size,
RUNTIME_distributed_barrier, so that MORSE does not hardcode the use of MPI
either.

This allows to use simgrid-mpi.

add MORSE_Pause/Resume function to avoid CPU consumption when no tasks have to be executed - call starpu_pause/resume, do nothing for quark (no need)

in MORSE_Desc_Create_User we can use the matrix in mat field without allocating it --> avoid to free it in this case, users could need it and will manage deallocation

change the way we include our own header files --> relative to the root - when plasma is in the same env, chameleon can take some headers not belonging to it (ex: #include descriptor.h, this file states in plasma install dir also) which make compilation errors

change installation directories for headers, executables and docs. Make it relative to chameleon to avoid a bloody mess in system dirs

change copyright - correct whitespace - place cmake module depending on chameleon in cmake_modules and no more in cmake_modules/morse